How do I turn the sound on/off?

Check the following:

Above the video, there is a speaker icon:

• Flashing Yellow Speaker Icon: the audio is streaming. Check your speakers, or message support for assistance.
• Blue Speaker Icon: Your audio is off on this lane. Click on the icon to turn it on.
• No Speaker Icon: This means that the auction has not turned on the stream. If bidding has started, click in the chat section to notify the block. If bidding has not started, please wait for the auction to turn it on.